# 14.2 Essential Questions What is Archimedes’ principle?

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14.2 Essential Questions What is Archimedes’ principle?
What is Pascal’s principle? What is Bernoulli’s principle? Copyright © McGraw-Hill Education Properties of Fluids

Archimedes’ Principle and Buoyancy
Despite their weight, ships are able to float. This is because a greater force pushing up on the ship opposes the weight—or force—of the ship pushing down. Buoyancy is the ability of a fluid—a liquid or a gas—to exert an upward force on an object immersed in it. Copyright © McGraw-Hill Education Properties of Fluids

Archimedes’ principle
In the third century B.C., a Greek mathematician named Archimedes made a discovery about buoyancy. Archimedes found that the buoyant force on an object is equal to the weight of the fluid displaced by the object. Copyright © McGraw-Hill Education Properties of Fluids

Density and buoyancy Suppose you form a steel block into the shape of a hull filled with air. The steel has the same mass but takes up a larger volume. The overall density of the steel boat and air is less than the density of water. The boat will now float. Copyright © McGraw-Hill Education Properties of Fluids

Density and buoyancy Animation FPO Add link to concepts in motion animation from page 442 here. Copyright © McGraw-Hill Education Properties of Fluids

Pascal’s Principle and Pressure
Pressure is force exerted per unit area. Blaise Pascal ( ), a French scientist, discovered a useful property of fluids. According to Pascal’s principle, pressure applied to a fluid is transmitted throughout the fluid. Copyright © McGraw-Hill Education Properties of Fluids

Pressure Pressure is the amount of force exerted per unit of area, or P = F/A. A balloon and a bicycle tire are considered to be containers. They remain inflated because of collisions the air particles have with the walls of their container. The collection of forces, caused by the collisions of the particles, pushes the walls of the container outward. If more air is pumped into the balloon, the number of air particles is increased. This causes more collisions with the walls of the container, which causes it to expand. Copyright © McGraw-Hill Education Properties of Fluids

Pressure Pressure is measured in a unit called Pascal (Pa), the SI unit of pressure. Because pressure is the amount of force divided by area, one pascal of pressure is one Newton per square meter or 1 N/m2. At sea level, atmospheric pressure is kPa. At Earth’s surface, the atmosphere exerts a force of about 101,300 N on every square meter—about the weight of a large truck. Copyright © McGraw-Hill Education Properties of Fluids

Pascal’s principle Hydraulic machines are machines that move heavy loads in accordance with Pascal’s principle. Maybe you’ve seen a car raised using a hydraulic lift in an auto repair shop. A pipe that is filled with fluid connects small and large cylinders. Pressure applied to the small cylinder is transferred through the fluid to the large cylinder. Copyright © McGraw-Hill Education Properties of Fluids

Pascal’s principle Because pressure remains constant throughout the fluid, according to Pascal’s principle, more force is available to lift a heavy load by increasing the surface area. Pressure applied to the small cylinder is transferred through the fluid to the large cylinder. Copyright © McGraw-Hill Education Properties of Fluids

Bernoulli’s Principle
According to Bernoulli’s principle, as the velocity of a fluid increases, the pressure exerted by the fluid decreases. One way to demonstrate Bernoulli’s principle is to blow across the top surface of a sheet of paper. The paper will rise. The velocity of the air you blew over the top surface of the paper is greater than that of the quiet air below it. As a result, the air pressure pushing down on the top of the paper is lower than the air pressure pushing up on the paper. The net force below the paper pushes the paper upward. Another application of Bernoulli’s principle is the hose-end sprayer. Copyright © McGraw-Hill Education Properties of Fluids

Bernoulli’s Principle
Pushing the trigger on the sprayer attachment allows the water in the hose to flow at a high rate of speed, creating a low pressure area above the straw-like tube. The concentrated chemical solution is sucked up through the straw and into the stream of water. The concentrated solution is mixed with water, reducing the concentration to the appropriate level and creating a spray that is easy to apply. Copyright © McGraw-Hill Education Properties of Fluids

Viscosity Another property exhibited by fluid is its tendency to flow. The resistance to flow by a fluid is called viscosity. When a container of liquid is tilted to allow flow to begin, the flowing particles will transfer energy to the particles that are stationary. In effect, the flowing particles are pulling the other particles, causing them to flow, too. If the flowing particles do not effectively pull the other particles into motion, then the liquid has a high viscosity, or a high resistance to flow. If the flowing particles pull the other particles into motion easily, then the liquid has low viscosity, or a low resistance to flow. Copyright © McGraw-Hill Education Properties of Fluids

Review Essential Questions Vocabulary What is Archimedes’ principle?
What is Pascal’s principle? What is Bernoulli’s principle? Vocabulary buoyancy pressure viscosity Copyright © McGraw-Hill Education Properties of Fluids